The invention relates to a device for detecting non-recorded portions on a magnetic tape for use with a tape recorder or the like. More particularly, the invention relates to a circuit for preventing malfunctions for use in such a detecting device.
Conventional detecting devices of this general type operate in such a way that a signal recorded on the magnetic tape is reproduced by a reproduction magnetic head and the output signal from the magnetic head is amplified and then rectified and amplified again. A switching circuit is provided which is set to either the ON or OFF state depending on the output of the rectifying circuit. Non-recorded portions on the magnetic tape are indicated by the state of the output of the switching circuit. However, with the use of such a detecting device, detection of non-recorded portions on a magnetic tape is sometimes erroneously indicated in the case where a magnetic tape is recorded with only a small level differential between the recorded portions and the non-recorded portions of the magnetic tape. An example of such a magnetic tape is a micro-cassette tape which has an inherently small S/N ratio.